You can hide nail holes with a piece of soap!

For a white wall, take a piece of white soap and rub it on the necessary spot in circular motions. The nail marks will be almost impossible to detect. It will leave a soap smear but that can be quickly remedied with a wet cloth and a little washing.  For colored walls, soap comes in a  kaleidoscope of colors so match the color of the soap to the wall and it will work great.